Operating fluids, including but not limited to lubricating fluid, hydraulic fluid, and liquid fuels, are used in various mechanical assemblies to perform a particular task. For example, lubricating fluid is used within a mechanical assembly to provide cooling and lubrication to the parts. Hydraulic fluid is pressurized by a pump to actuate a piston in order to generate a moving force. And liquid fuels provide a source of potential energy to various types of fuel driven engines. These fluids are generally used in mechanical assemblies where the fluids come in contact, or otherwise interact with, various supply lines, valves, reservoirs, pumps, and engines, as well as various other mechanical assemblies. As a result of this interaction, wear particles generated by moving parts within the machine as well as contamination particles from outside the machine are present in the fluid. These particles by themselves are not a problem for the machine because they are being removed by the oil filter. However, they are an indication of the type of wear going on within the machine. By knowing the type of wear particles being generated and their size, concentration and trend, a prediction on the health of the machine can be made. By knowing the health of the machine, servicing need only be done when it is required: saving time, money, and increasing the life of the machine.
For example, lubricating fluid, such as oil, used by an operating machine, such as a combustion engine, is often contaminated by the result of: combustion by-products, debris that has entered the air intake of the engine, and other particles that are the result of the wear of the internal parts of the engine. In particular, these particles, which are typically on the order of about 150 microns or less, are indicative of the overall wear of the engine. Moreover, by analyzing the physical characteristics, such as the size and shape of the particles in real-time, the current wear or “health” of the engine can be identified on an on-demand basis.
As a result, several systems that directly analyze the various operating fluids of an engine or other operating machine have been developed. One method, referred to as the “offline” method involves extracting a sample of operating fluid, and then sending the sample to a remotely located laboratory for analysis. Although this system is effective, it is time consuming as the analysis requires a substantial lead time from the time the sample is taken and until wear results are obtained.
Recently, fluid analysis systems have been developed, which utilize laser optical near-field imaging techniques. These systems comprise a laser light source, a light detection device, a flow cell, and a pump or other means to draw the fluid through the flow cell. One such type of flow cell utilizing near-field imaging techniques is disclosed in U.S. Pat. No. 6,104,483, which is incorporated herein by reference. This system determines the number of particles in the fluid, and then identifies the size and physical characteristics of the particle. Because the physical characteristics of a particle directly correspond to a particular wear mechanism or phenomena, the system can correlate the detected particle characteristics with the particular mechanism causing the wear, such as metal particles created by engine wear or debris entering through the air intake of an engine. As such, the system informs the user as to the source of the particles, thereby enabling the user to more accurately diagnose and remedy any engine problems that may exist.
Although the utilization of laser optical near-field imaging techniques provided by the flow cell have proven to be a significant advance in the prospect of real-time wear analysis, such systems are plagued by various limitations. For example, while manufacturers have overcome the technical obstacles associated with the operation of the flow cell at high temperature and/or high pressure, they have been unable to provide a flow cell that has a compact dimension, is lightweight, and cost effective, and which is able to maintain a laminar flow of the operating fluid therethrough. A laminar flow is advantageous in that it allows wear particles to pass uniformly through the flow cell, allowing a fluid analysis system to more accurately characterize the shape of the wear particles.
Therefore, there is a need in the art for an optical flow cell that is configured to provide laminar flow of the operating fluid passing therethrough. Moreover, there is a need in the art for an optical flow cell that is configured to withstand environments having high pressure and/or high temperature, while providing laminar flow to the operating fluid passing therethrough.